Sanicro® 28 (UNS N08028) is a high-alloy austenitic stainless steel designed for service in highly aggressive and corrosive environments. Developed as a material to resist corrosion attack in phosphoric acid processing, the grade's chemical composition ensures superior performance in a wide range of demanding conditions.
Sanicro® 28 offers excellent corrosion resistance in, for example, caustic and acidic applications including sulphuric and high chloride environments. It can also be used at elevated temperatures.
Sanicro® 28 is widely used, for example, in hydrogen sulfide containing environments within the oil and gas industry. This is due to the material's excellent resistance to sulfide cracking in conditions characterized by high levels of hydrogen sulfide (H2S), carbon dioxide (CO2) and chlorides (Cl-). Examples of applications are production tubing (OCTG) and heat exchangers used in the processing of sour crude.
The combination of molybdenum and nickel in Sanicro 28 helps prevent cracking caused by polythionic acid attack during equipment start up and shut down. The grade is also utilized in oil refineries to reduce the effects of naphthenic acid corrosion.
A large Indian oil company decided to expand one of its refineries with a new coker unit, where residual oil is cracked into lower molecular weight hydrocarbons. The process is rich in hydrogen sulfide (H2S), which makes it extremely corrosive and increases the risk of hydrogen induced cracking. The engineering company involved in the plant design specified tubes made from Sanicro® 28.
The new refinery started up in 2005. In 2010, the heat exchangers were opened and the Sanicro® 28 tubes were inspected both visually and by non-destructive eddy current testing. There were no signs of corrosion.